Preparation of branched siloxane

Abstract

By reacting a branched siloxane compound of formula (2) containing compounds of formula (1) as an impurity with a disiloxane compound of formula (3) in the presence of an acid compound, there is prepared a branched siloxane of formula (2) containing a reduced level of compounds of formula (1). R 1 n Si(OSiR 2 3 ) 3-n (OR 3 )  (1) R 1 n Si(OSiR 2 3 ) 4-n   (2) R 2 3 SiOSiR 2 3   (3) R 1 is a monovalent hydrocarbon group, R 2 and R 3 are H or monovalent hydrocarbon groups, and n is 0 or 1.

1. A method for preparing a branched siloxane of the general formula (2), comprising the step of:
 reacting a branched siloxane compound of the general formula (2) containing a compound of the general formula (1) as an impurity with a disiloxane compound of the general formula (3) in the presence of an acid compound, for forming a branched siloxane of formula (2) containing a reduced level of the compound of formula (1), 
   R 1   n Si(OSiR 2   3 ) 3-n (OR 3 )  (1)  
 
 
       wherein R 1  is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 20 carbon atoms, R 2  and R 3  are selected from hydrogen and substituted or unsubstituted monovalent hydrocarbon groups of 1 to 20 carbon atoms, R 2  may be the same or different, n is equal to 0 or 1,
   R 1   n Si(OSiR 2   3 ) 4-n   (2)  
 
       wherein R 1 , R 2  and n are as defined above,
   R 2   3 SiOSiR 2   3   (3)  
 
       wherein R 2  is as defined above. 
     
     
       2. The method of  claim 1 , wherein the acid compound is used in at least an equimolar amount relative to the total of the compound of formula (1). 
     
     
       3. The method of  claim 1 , wherein the branched siloxane compound of formula (2) containing the compound of formula (1) as an impurity has been synthesized by reacting a disiloxane compound of formula (3) with an organoxysilane compound of the general formula (4):
   R 1   n Si(OR 4 ) 4-n   (4)  
 
       wherein R 1  is as defined above, R 4  is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 20 carbon atoms, and n is equal to 0 or 1, in the presence of an acid catalyst. 
     
     
       4. The method of  claim 3 , wherein the branched siloxane compound of formula (2) containing the compound of formula (1) as an impurity has been synthesized by adding the organoxysilane compound of formula (4) to a liquid mixture of the disiloxane compound of formula (3), an alcohol and the acid catalyst for reaction, and further adding water for effecting co-hydrolysis. 
     
     
       5. The method of  claim 1 , wherein the branched siloxane compound of formula (2) is selected from the group consisting of methyltris(trimethylsiloxy)silane, tetrakis(trimethylsiloxy)silane, 3-acryloxypropyltris(trimethylsiloxy)silane, 3-methacryloxypropyltris(trimethylsiloxy)silane, p-styryltris(trimethylsiloxy)silane, 5-norbornenyltris(trimethylsiloxy)silane, 2-(5-norbornenyl)ethyltris(trimethylsiloxy)silane, and 2-(5-norbornenyl)ethyltris(dimethylvinylsiloxy)silane. 
     
     
       6. The method of  claim 1 , wherein the acid compound is sulfuric acid.